Seismic control bearing device and seismic control system including the same

ABSTRACT

Provided are a seismic control bearing device capable of absorbing and/or blocking vibration energy transmitted to structures due to earthquakes, and so on, as well as actively controlling various dynamic behaviors generated from the structures with low power and without additional equipment, and a seismic control system including the same. The seismic control bearing device is installed between a ground base and a structure constructed on the ground base to reduce vibration energy applied to the structure, and includes a plurality of deposition members spaced apart from each other; and a plurality of magneto-sensitive members disposed between the deposition members and formed of a magneto-sensitive material. The properties including a stiffness coefficient and an damping coefficient of the magneto-sensitive material are varied depending on a variation of a magnetic field formed around the magneto-sensitive member.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2006-0052880, filed on Jun. 13, 2006, the disclosure of which ishereby incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a seismic control bearing device and aseismic control system including the same, and more particularly, to aseismic control bearing device installed in structures such asbuildings, bridges, and so on, and capable of reducing vibration energytransmitted to the structures by seismic load, and a seismic controlsystem including the same.

2. Description of the Related Art

In recent times, research on seismic isolation devices has been widelyattempted to protect structures such as buildings, bridges, and so on,by absorbing and/or blocking vibration energy applied to the structuresusing additional equipment. A base isolation device such as an elastomerbearing, a lead rubber bearing, a sliding bearing, and so on has beendeveloped as a representative seismic isolation device. FIG. 1illustrates a lead rubber bearing 1 installed between a ground base 50and a structure 60.

However, a seismic-resistant design using the seismic isolation deviceincreases a natural frequency of a structure system, constituted of abase isolation device and a structure to increase relative displacementresponse of the structure, thereby causing disadvantages in usabilityand design of the base isolation device. In addition, it is known thatthe above seismic-resistance design is inappropriate for broad inputearth movement due to dynamic characteristics having strongnon-linearity. For example, a base isolation device designed for the ElCentro Earthquake may not show seismic isolation performance when apredominant frequency of seismic load is varied, a seismic center isnear, a wave velocity is fast, and a seismic cycle is large, like theMexico City earthquake.

Recently, a hybrid controller combining a base isolation device with anactive device has been developed. The hybrid controller can effectivelyreduce vibration energy of various input loads in comparison with amanual controller. In addition, the hybrid controller can also control amulti-vibration mode of the structure. However, addition of the activecontroller can increase costs because of high-capacity external power,and it is difficult to obtain reliability of equipment for a long time.

On the other hand, since a semi-active controller using a control fluidprovides performance similar to the active controller and requires smallelectric power, vibration control devices using an electro-rheological(ER) fluid and a magneto-rheological (MR) fluid have been developedsince 1992, and functionality of the semi-active controller has beenconfirmed through small-scale model experiments. Especially, an MR fluiddamper that can operate with a lower power than an ER fluid damper hasbeen continuously researched since 1994. Recently, equipment of about20-ton size has been developed. However, as shown in FIG. 2, since thesemi-active controller, for example, the MR fluid damper 2, should beinstalled with the base isolation device such as the lead rubber bearing1, it is difficult to adapt the MR fluid damper to an actual structurefor economic reasons.

SUMMARY OF THE INVENTION

An embodiment of the invention provides a seismic control bearing devicecapable of absorbing and/or blocking vibration energy transmitted tostructures due to earthquakes, and so on, as well as activelycontrolling various dynamic behaviors generated from the structures withlow power and without additional equipment, and a seismic control systemincluding the same.

In one aspect, the invention is directed to a seismic control bearingdevice installed between a ground base and a structure constructed onthe ground base to reduce vibration energy applied to the structure. Theseismic control bearing device includes a plurality of depositionmembers spaced apart from each other; and a plurality ofmagneto-sensitive members disposed between the deposition members andformed of a magneto-sensitive material. The properties including astiffness coefficient and an damping coefficient of themagneto-sensitive material are varied depending on a variation of amagnetic field formed around the magneto-sensitive material.

In another aspect, the invention is directed to a seismic control systemincluding: a sensing unit for sensing dynamic behavior of a structureand outputting a sensing signal corresponding to dynamic vibration ofthe structure; a seismic control bearing device installed between thestructure and a ground base, on which the structure is constructed, toreduce vibration energy applied to the structure, wherein the seismiccontrol bearing device includes a plurality of deposition members spacedapart from each other; and a plurality of magneto-sensitive membersdisposed between the deposition members and formed of amagneto-sensitive material; a magnetic field forming unit for generatinga variation of a magnetic field in the seismic control bearing devicesuch that the properties including a stiffness coefficient and andamping coefficient of the magneto-sensitive material are varieddepending on the variation of the magnetic field; and a control unit forreceiving a sensing signal from the sensing unit to control the magneticfield forming unit such that the seismic control bearing devicegenerates a seismiccontrol force for reducing vibration energy of thestructure on the basis of the sensing signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will become more apparent from the following more particulardescription of exemplary embodiments of the invention and theaccompanying drawings. The drawings are not necessarily to scale,emphasis instead being placed upon illustrating the principles of theinvention.

FIG. 1 is a schematic cross-sectional view of a conventional seismicisolation bearing device installed in a structure.

FIG. 2 is a schematic cross-sectional view of a conventionalmagneto-rheological (MR) damper installed in a structure with a seismicisolation bearing device.

FIG. 3 is a schematic cross-sectional view of a seismic control bearingdevice installed in a structure in accordance with an exemplaryembodiment of the present invention.

FIG. 4 is a schematic cross-sectional view of a magnetic field formed inthe seismic control bearing device shown in FIG. 3.

FIG. 5 is an enlarged view of portion “A” of FIG. 4.

FIG. 6 is a schematic block diagram of a seismic control systemincluding the seismic control bearing device in accordance with anexemplary embodiment of the present invention.

FIG. 7 is a schematic cross-sectional view of a seismic control bearingdevice in accordance with another exemplary embodiment of the presentinvention.

FIG. 8 is a view showing a dynamic model of a base isolation device.

FIG. 9 is a schematic view of a five-floor building having six degreesof freedom.

FIG. 10 is a graph showing ground acceleration and Fast FourierTransform of the El Centro Earthquake.

FIG. 11 is a graph showing ground acceleration and Fast FourierTransform of the Kobe Earthquake.

FIG. 12 is a graph showing ground acceleration and Fast FourierTransform of the Northridge Earthquake.

FIG. 13 is a graph showing dynamic behavior of the El Centro Earthquake.

FIG. 14 shows a displacement-force curve of the El Centro Earthquake.

FIG. 15 is a graph showing dynamic behavior of the Kobe Earthquake.

FIG. 16 shows a displacement-force curve of the Kobe Earthquake.

FIG. 17 is a graph showing dynamic behavior of the NorthridgeEarthquake.

FIG. 18 shows a displacement-force curve of the Northridge Earthquake.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown.

FIG. 3 is a schematic cross-sectional view of a seismic control bearingdevice installed in a structure in accordance with an exemplaryembodiment of the present invention, FIG. 4 is a schematiccross-sectional view of a magnetic field formed in the seismic controlbearing device shown in FIG. 3, FIG. 5 is an enlarged view of portion“A” of FIG. 4, and FIG. 6 is a schematic block diagram of a seismiccontrol system including the seismic control bearing device inaccordance with an exemplary embodiment of the present invention.

Referring to FIGS. 3 to 6, a seismic control system 100 in accordancewith an exemplary embodiment of the present invention includes a pair ofseismic control bearing devices 10, a magnetic field forming unit 20, asensing unit 30, and a control unit 40.

As shown in FIG. 3, each bearing device 10 is installed between a groundbase 50 and a structure 60. The structure 60, for example, a building, abridge, and so on, is constructed on the ground base 50. The ground base50 is generally installed on the ground 51 using concrete, etc. Theseismic control bearing device 10 functions to block direct transmissionof an earthquake occurring from the seismic center to the structure 60and to absorb vibrations generated from the earthquake. The seismiccontrol bearing device 10 includes a plurality of deposition members 11and a plurality of magneto-sensitive members 12.

The deposition members 11 are disposed apart from each other. Each ofthe deposition members 11 is formed of a plate-shaped metal member, forexample, a steel plate.

The magneto-sensitive members 12 are disposed between the depositionmembers 11. Each of the magneto-sensitive members 12 has a plate shape,similar to the deposition member 11. Each magneto-sensitive member 12 isformed of a magneto-sensitive material, in which the properties such asa stiffness coefficient and an damping coefficient are varied dependingon a variation of the magnetic field. The magneto-sensitive materialincludes a rubber matrix 121 and metal particles 122. The rubber matrix121 may be formed of rubber, for example, natural rubber, polyurethane,and so on. The metal particles 122 are formed of a metal material suchas iron particles, and dispersed in the rubber matrix 121. In theembodiment the magneto-sensitive material is manufactured by evenlymixing natural rubber with iron particles at about 120° C., filling themixture into a mold, and curing the mixture under an electro-magneticfield of 0.7 T for thirty minutes.

The properties of the magneto-sensitive material vary depending on avariation of a magnetic field formed around the magneto-sensitive member12. That is, as shown by an arrow in FIG. 4, when the magnetic field isformed around the magneto-sensitive member 12, the metal particles 122dispersed in the rubber matrix are re-aligned to a direction of themagnetic field to vary the properties of the magneto-sensitive materialsuch as a stiffness coefficient, an damping coefficient, and so on. Forexample, when the strength and/or direction of the magnetic field arevaried, the stiffness coefficient and the damping coefficient of themagneto-sensitive member 12 are also varied. As described above, thevariation of the properties of the magneto-sensitive material wasintroduced by Jacob Rainbow in 1948. In addition, the above variation isdisclosed in the papers of Kordonsky, W. (1993), “Magneto-rheologicaleffects as a base of new devices and technologies”, J. Mag. & Mag. Mat,Vol. 122, pp. 395-398; Jolly, M. R., Carlson, J. D. and Munoz, B. C.(1996), “A model of the behavior of magneto-rheological materials”,Smart Material Structures, Vol. 2, pp. 607-614; Carlson J. D. and JollyM. R. (2000), “MR fluid, form and elastomer devices”, Mechatronics, Vol.10, pp. 55-69, and so on.

The magnetic field forming unit 20 generates a variation of the magneticfield in the seismic control bearing device 10. The magnetic fieldforming unit 20 includes a coil member 21 and a current supply part 22.The coil member 21 has an annular shape to surround the seismic controlbearing device 10. The current supply part 22 supplies current to thecoil member 21. When current is applied to the coil member 21, amagnetic field is formed around the coil member 21, as shown in FIG. 4.

The sensing unit 30 is attached to the structure 60 to sense dynamicvibrations of the structure 60. In addition, the sensing unit 30 outputsa sensing signal corresponding to dynamic behavior of the structure 60as an electrical signal. The sensing signal includes displacement,acceleration, ground acceleration, and a vibration cycle of thestructure. More specifically, the sensing signal includes horizontaldisplacement, horizontal acceleration, horizontal ground acceleration,and a horizontal vibration cycle of the structure. In addition, thesensing unit 30 continuously outputs sensing signals corresponding tothe dynamic behavior of the structure until the earthquake isdisappeared after the earthquake occurs.

The control unit 40 controls the magnetic field forming unit 20 tocontrol a magnetic field formed around the seismic control bearingdevice 10. First, the control unit 40 receives a sensing signal from thesensing unit 30. Next, the control unit 40 calculates a seismic controlforce for reducing vibration energy generated from the structure 60 onthe basis of the sensing signal. Preferably, the control unit 40calculates a control force that can minimize the vibration energygenerated from the structure. More specifically, the control force iscalculated by minimizing a performance index J, which will be describedin the following description of numerical analysis. In the embodiment,the control unit 40 is configured to include a linear quadratic (LQ)regulator, which is well known. As described above, after calculatingand setting the control force, the control unit 40 controls the magneticfield forming unit 20 to drive the seismic control bearing device 10 togenerate the control force. Here, since the properties of the seismiccontrol bearing device 10, especially, a stiffness coefficient and andamping coefficient of the magneto-sensitive member 12 are varieddepending on a variation of the magnetic field formed around the seismiccontrol bearing device 10, the control unit 40 controls the seismiccontrol bearing device 10 to perform the calculated control force byforming an appropriate magnetic field in the seismic control bearingdevice 10. That is, the control unit 40 controls an amount of currentsupplied from the current supply part 22 to control the strength of amagnetic field formed around the coil member 21, thereby adjusting thecontrol force of the seismic control bearing device 10.

For example, the control unit 40 controls the current supply part 22 notto supply current during normal times when there is no seismic wavetransmitted to the structure 60. In addition, when a seismic wave istransmitted to the structure 60, the control unit 40 calculates acontrol force for minimizing vibration energy of the structure 60 on thebasis of the sensing signal, and appropriately controls an amount ofcurrent supplied to the coil member 21 from the current supply part 22to vary the strength of a magnetic field formed around the seismiccontrol bearing device 10, thereby controlling the seismic controlbearing device 10 to perform the control force. Therefore, it ispossible to actively control dynamic behavior of the structure due tothe earthquake. In addition, the control unit 40 controls supply ofcurrent of the current supply part 22 corresponding to the sensingsignal continuously input until the earthquake is disappeared after theearthquake occurs, thereby controlling the dynamic behavior of thestructure 60 until the earthquake is disappeared after the earthquakeoccurs.

Hereinafter, in the seismic control system 100 in accordance with anexemplary embodiment of the present invention, when a dynamic load dueto the earthquake is applied to the structure 60, an example of aprocess of reducing vibration energy of the structure 60 and controllingdynamic behavior of the structure will be described with reference toFIG. 6. Dotted arrows shown in FIG. 6 represent a moving path ofvibration energy due to the earthquake, sensing of dynamic behavior ofthe structure, and a control force of the seismic control bearing device10.

During normal times when there is no earthquake, since the control unit40 controls the current supply part 22 not to supply current to the coilmember 21, there is no magnetic field generated around the seismiccontrol bearing device 10. When an earthquake occurs in this state,current is applied to the coil member 21 at substantially the same timethe earthquake occurs to form a magnetic field around the coil member21. The magnetic field provides a control force such that the seismiccontrol bearing device 10 can minimize vibration energy of the structure60, thereby optimally controlling dynamic behavior of the structure 60,which will be described in detail.

When an earthquake occurs, the sensing unit 30 attached to the structure60 senses horizontal displacement, horizontal acceleration, horizontalground acceleration, and a horizontal vibration cycle of the structure60, and outputs a sensing signal including the displacement,acceleration, ground acceleration and vibration cycle to the controlunit 40 as an electrical signal. The control unit 40 calculates acontrol force that can minimize vibration energy of the structure 60 onthe basis of the sensing signal, and then determines the strength of amagnetic field to be formed around the seismic control bearing device 10to perform the control force. Next, the control unit 40 controls anamount of current supplied to the coil member 21 from the current supplypart 22 to form the magnetic field. As described above, when the currentis supplied to the coil member 21, as shown in FIG. 4, a magnetic fieldis formed around the seismic control bearing device 10 to re-align themetal particles dispersed in the magneto-sensitive material in adirection of the magnetic field. As a result of the realignment of themetal particles, the properties of the magneto-sensitive material, i.e.,a stiffness coefficient and an damping coefficient are varied to varyseismic control performance of the seismic control bearing device 10. Asdescribed above, when the properties of the magneto-sensitive materialvary depending on a variation of the magnetic field, it is possible toactively control various types of vibrations applied to the structure60. Especially, there is no need to use a large amount of power, unlikethe conventional active control system. In addition, it is possible toaccomplish the same semi-active control and base isolation performanceas the conventional art through a single seismic control bearing device10, unlike the conventional system including the semi-active controllerand the base isolation device.

Meanwhile, the control unit 40 controls current supply of the currentsupply part 22 corresponding to the sensing signal continuously inputuntil the earthquake is disappeared after the earthquake occurs, to varythe seismic control performance of the seismic control bearing device 10to correspond to the sensing signal, thereby continuously controllingdynamic behavior of the structure 60 until the earthquake is disappearedafter the earthquake occurs.

As described above, the seismic control bearing device 10 in accordancewith an exemplary embodiment of the present invention absorbs and/orblocks vibration energy transmitted to the structure due to sheardeformation, similar to the conventional base isolation device, forexample, the lead rubber bearing. In addition, adjustment of thestrength of the magnetic field varies properties of the seismic controlbearing device 10, for example, a stiffness coefficient and an dampingcoefficient, thereby enabling semi-active control of dynamic behavior ofthe structure.

Meanwhile, numerical analysis for checking seismic control performanceof the seismic control system including the seismic control bearingdevice in accordance with an exemplary embodiment of the presentinvention was performed. The numerical analysis was performed for afive-floor building having six degrees of freedom used by Kelly et al.in 1987. In addition, evaluation of performance and semi-active controlof the seismic control system as a base isolation device was performedby obtaining responses of the seismic control system to the El CentroEarthquake, the Kobe Earthquake, and the Northridge Earthquake, eachhaving different characteristics. Further, in order to analyzeeffectiveness of the base isolation device, the numerical analysis wasperformed with respect to the following three cases, 1) a structurewhich is uncontrolled and base-supported, 2) a structure in which a leadrubber bearing is installed, and 3) a structure in which a seismiccontrol bearing device is installed.

First, an equation of motion of the base isolation device such as theseismic control bearing device and the conventional lead rubber bearingis obtained. As shown in FIG. 8, an equation of motion of a model, fromwhich the ground base and the structure are separated, is calculated asfollows.

M{umlaut over (x)}+C{dot over (x)}+Kx=Λf−M{umlaut over (x)} _(g)

Here, f and Λ=[1 0]^(T) represent an additional force by the baseisolation device and a position vector. x _(g) represents a seismicload, and x=[x_(b)x_(s)]^(T) represents displacement of the ground baseand the structure. In addition, matrix of mass M, damping C andstiffness K is as follows.

${M = \begin{bmatrix}m_{b} & 0 \\0 & m_{s}\end{bmatrix}},\mspace{14mu} {C = \begin{bmatrix}{c_{b} + c_{s}} & {- c_{s}} \\{- c_{s}} & c_{s}\end{bmatrix}},\mspace{14mu} {K = \; \begin{bmatrix}{k_{b} + k_{s}} & {- k_{s}} \\{- k_{s}} & k_{s}\end{bmatrix}}$

Here, m_(b) and m_(s) represent masses of the ground base and thestructure, c_(b) and k_(b) represent an damping coefficient and astiffness coefficient of the ground base, and c_(s) and k_(s) representan damping coefficient and a stiffness coefficient of the structure.

A state parameter q is defined as q=[x^(T){dot over (x)}^(T)]^(T) torepresent the base isolation device as the following state spatialequation

{dot over (q)}=Aq+Bf+E{umlaut over (x)} _(g)

Here, A, B and E represent a system matrix, a control matrix, and adisturbance matrix, which are as follows.

${A = \begin{bmatrix}0 & I \\{{- M^{- 1}}K} & {{- M^{- 1}}C}\end{bmatrix}},\mspace{14mu} {B = \begin{bmatrix}0 \\{{- M^{- 1}}A}\end{bmatrix}},\mspace{14mu} {E = {\begin{bmatrix}0 \\{- 1}\end{bmatrix}.}}$

Next, as shown in FIG. 9, the structure, in which the seismic controlbearing device in accordance with the present invention is installed,was modeled as a five-floor building. Mass, a stiffness coefficient, andan damping coefficient of the five-floor building are as described inTable 1. The uncontrolled and base fixed structure has an damping of 2%and a natural frequency of 0.3 seconds in a first mode. While dynamicnon-linearity of the structure was ignored, excessive structuralmovement was substantially considered.

TABLE 1 Mass of each floor Stiffness of each Damping of each Position[kg] floor [kN/m] floor [kNs/m] Ground base m_(b) = 6800 k_(b) = 231.5c_(b) = 3.74 First floor m₁ = 5897 k₁ = 33732 c₁ = 67 Second floor m₂ =5897 k₂ = 29093 c₂ = 58 Third floor m₃ = 5897 k₃ = 28621 c₃ = 57 Fourthfloor m₄ = 5897 k₄ = 24954 c₄ = 50 Fifth floor m₅ = 5897 k₅ = 19059 c₅ =38

In addition, the lead rubber bearing was designed to have a yield forceof 14.38 kN. A hysteresis restoring force f_(LRB) and a non-dimensionalhysteresis parameter z to be used in the numerical analysis are obtainedby the following formulae.

f _(LRB) =Q _(pb) +k _(b) x _(b) +c _(b) {dot over (x)} _(b)

ż=−γ|{dot over (u)} _(b) |z|z| ^(n−1) −β{dot over (u)} _(b) |z| ^(n)+A{dot over (u)} _(b)

Here, Q_(pb) is a yield load of lead, and is obtained byQ_(pb)=(1−K_(yield)/K_(initial))·Q_(y). Q_(y) is assumed as 5% of thetotal weight of the structure, and parameter values used in the leadrubber bearing, for example, a stiffness ratio of before/after yield oflead β, γ, a non-dimensional parameter A, an integer coefficient n isused for design parameters described in Table 2, as disclosed in Ramallo(2002), “Smart” Base Isolation Systems (2002) Journal of EngineeringMechanics Vol. 128. No. 10 pp. 1088-1099.

TABLE 2 Parameter Value Parameter Value Qpb 14.48(kN) γ 38.37 Qy18.14(kN) A 76.74 K_(yield)/K_(initial) 6 n 1 β −38.37

Next, in order to enable semi-active control of the seismic controlbearing device, an active controller was first designed. In order todesign the active controller, Q and R values were obtained to minimize aperformance index J.

J = ∫₀^(∞)(z^(T)Qz + F^(T) RF)t

The Q value and the R value were obtained through a trial and errormethod and used as follows.

$\begin{matrix}{R = \frac{1}{\left( {22{kN}} \right)^{2}}} \\{{= \frac{1}{(22000)^{2}}},}\end{matrix}\mspace{14mu}$ $Q = {{diag}\begin{pmatrix}{q_{drifts}^{\prime}I} & 0 \\0 & {q_{accels}^{\prime}I}\end{pmatrix}}$ Here, q_(drifts)^(′) = 33.1,  q_(accels)^(′) = 99.3

In addition, in order to convert the active controller into thesemi-active controller, when the magnetic field is not applied, a basicdamping force of the seismic control bearing device was set as 1 kN, andwhen the magnetic field is applied, a maximum damping force of seismiccontrol bearing device was set as 200 kN, using a clipped-optimalcontrol algorithm.

Finally, a seismic load to be input into the structure was set as threetypes, i.e., the El Centro Earthquake, the Kobe Earthquake, and theNorthridge Earthquake. The El Centro Earthquake is a first severeearthquake recorded by an accelerometer and has been considered as areference earthquake for research and designs of a seismic-resistantdesign standard or a base isolation device. The Kobe Earthquake is anearthquake in a sedimentary ground similar to the Mexico City, a shallowearthquake generated from underground of about 20 km, and a typicalsevere earthquake occurring just below the city and having a maximumground acceleration of 0.83 g. The Northridge Earthquake was a severeearthquake with a magnitude of 6.8 which generated by reverse faultmovement. The Northridge Earthquake became a direct cause for currentlyperformed worldwide seismic design development.

As described above, after preparing the numerical analysis, performanceof the conventional lead rubber bearing and the seismic control bearingdevice was evaluated. In the numerical analysis, accelerogram and FastFourier Transform (FFT) of the respective earthquakes used in an inputseismic load are described in FIGS. 10 to 12, and properties of therespective earthquakes are described in Table 3.

TABLE 3 Recording Predominant Date of Time Frequency PGA EarthquakeOccurrence (sec) (Hz) Magnitude (g) El Centro 1940.5.18 50 1.5 7.1 0.35Kobe 1995.1.17 50 1.3 7.2 0.833 Northridge 1994.1.17 40 0.63 6.8 0.843

Performing the numerical analysis through the above processes andcomparing performance of the seismic control bearing device and the leadrubber bearing, showing their ability in the El Centro Earthquake, theKobe Earthquake, and the Northridge Earthquake, when strength of maximumground acceleration is applied, with maximum base displacement, maximumacceleration of the uppermost floor, and relative displacement betweenfirst and second floors, the following result can be obtained. In FIGS.13 to 18, LRB represents the result of the structure in which the leadrubber bearing is installed, Active represents the result of theactive-controlled structure, Fixed represents the result of thestructure to which the ground base is fixed, and MS rubber representsthe result of the structure in which the seismic control bearing devicein accordance with an exemplary embodiment of the present invention isinstalled.

First, reviewing dynamic behavior of the El Centro Earthquake, as shownin FIG. 13, the seismic control bearing device has a base displacementof 28 cm smaller than 30 cm of the lead rubber bearing by about 2 cm.The seismic control bearing device has an uppermost floor accelerationof 0.191 g, which is reduced by about 84% in comparison with the basefixed structure, and the lead rubber bearing has an uppermost flooracceleration of 0.542 g, which is reduced by about 55% in comparisonwith the base fixed structure. The seismic control bearing device has arelative displacement between first and second floors of 1.5 mm, whichis reduced by 80% or more in comparison with the base fixed structure,and the lead rubber bearing has a relative displacement between firstand second floors of 2.7 mm, which is reduced by about 68% or more incomparison with the base fixed structure. As described above, it will beappreciated that the seismic control bearing device has a betterrelative displacement between floors than the lead rubber bearing.

In addition, FIG. 14 illustrates the relationship between displacementand damping force of the lead rubber bearing and the seismic controlbearing device in the El Centro Earthquake. The lead rubber bearing hasan damping force of about 80.94 kN, and the seismic control bearingdevice has an damping force of about 119 kN.

Next, base displacement, uppermost floor acceleration, and relativedisplacement between first and second floors of the Kobe Earthquake as anear earthquake were compared. As shown in FIG. 15, the seismic controlbearing device has a base displacement of 36.1 cm smaller than 43.3 cmof the lead rubber bearing by about 7 cm. The seismic control bearingdevice has an uppermost floor acceleration of 0.244 g, which is reducedby about 92% in comparison with the base fixed structure, and the leadrubber bearing has an uppermost floor acceleration of 0.372 g, which isreduced by about 88% in comparison with the base fixed structure. Theseismic control bearing device has a relative displacement between firstand second floors of 1.95 mm, which is reduced by 90% or more incomparison with the base fixed structure, and the lead rubber bearinghas a relative displacement between first and second floors of 9.61 mm,which is reduced by about 50% or more in comparison with the base fixedstructure. As described above, it will be appreciated that the seismiccontrol bearing device has a better relative displacement between floorsthan the lead rubber bearing.

FIG. 16 illustrates the relationship between displacement and dampingforce of the lead rubber bearing and the seismic control bearing devicein the Kobe Earthquake. The lead rubber bearing has a maximum dampingforce of about 98.98 kN, and the seismic control bearing device has amaximum damping force of about 190.57 kN.

Finally, base displacement, uppermost floor acceleration, and relativedisplacement between first and second floors of the NorthridgeEarthquake were compared. As shown in FIG. 17, the seismic controlbearing device has a base displacement of 81 cm smaller than 97.9 cm ofthe lead rubber bearing by about 17 cm. The seismic control bearingdevice has an uppermost floor acceleration of 0.543 g, which is reducedby about 86% in comparison with the base fixed structure, and the leadrubber bearing has an uppermost floor acceleration of 0.815 g, which isreduced by about 80% in comparison with the base fixed structure. Theseismic control bearing device has a relative displacement between firstand second floors of 4.3 mm, which is reduced by 83% or more incomparison with the base fixed structure, and the lead rubber bearinghas a relative displacement between first and second floors of 6.6 mm,which is reduced by about 74% or more in comparison with the base fixedstructure.

FIG. 18 illustrates the relationship between displacement and dampingforce of the lead rubber bearing and the seismic control bearing devicein the Northridge Earthquake. The lead rubber bearing has a maximumdamping force of about 204.98 kN, and the seismic control bearing devicehas a maximum damping force of about 341.17 kN.

Entirely reviewing the above results, as shown in Tables 4 and 5, itwill be appreciated that the seismic control bearing device inaccordance with the present invention has a remarkably betterperformance in all kinds of earthquakes than the conventional leadrubber bearing.

TABLE 4 Seismic control bearing Base fixed Lead rubber bearing device ElEl El Centro Kobe Northridge Centro Kobe Northridge Centro KobeNorthridge Maximum — — — 0.305 0.433 0.979 0.282 0.361 0.811 basedisplacement Uppermost 1.197  2.986 4.008  0.542 0.372 0.815 0.191 0.2440.543 floor acceleration (g) Relative 0.00836 0.019 0.0251 0.002770.0096 0.0066 0.0015 0.002 0.0043 displacement between first and secondfloors

TABLE 5 Relative Maximum Uppermost displacement base maximum betweenfirst and displacement acceleration second floors Seismic SeismicSeismic control control control bearing bearing bearing Earthquake LRBdevice LRB device LRB device El Centro —  7% (55%) 65%(84%) (68%)46%(80%) (0.350 g) Kobe — 17% (88%) 34%(92%) (50%) 79%(90%) (0.83 g)Northridge — 17% (80%) 33%(86%) (74%) 35%(83%) (0.843 g) *Numbers in ( )represent response reduction effect of the base fixed structure.

While the seismic control bearing device in accordance with the presentinvention includes a plurality of deposition members and a plurality ofmagneto-sensitive members, a seismic control bearing device 10 a may beconfigured as shown in FIG. 7. That is, the seismic control bearingdevice 10 a may further include a core member 13, different from FIG. 4.The core member 13 is configured to pass through the deposition members11 and the magneto-sensitive members 12. In addition, the core member 13is formed of a metal member such as lead. The core member 13 functionsto absorb vibrations applied to the structure 60.

Exemplary embodiments of the present invention have been described, butare not limited thereto. In addition, various modifications may be madeby those skilled in the art.

For example, in the embodiment, while the seismic control bearing deviceof the present invention is configured such that the strength of amagnetic field is varied depending on a variation of an amount ofcurrent and properties of the magneto-sensitive material are varieddepending on the variation of the strength of the magnetic field, theproperties of the magneto-sensitive material may be varied by changing adirection of the magnetic field formed around the seismic controlbearing device.

In addition, in the embodiment, while a single core member is disposed,a plurality of coil members may be disposed around the seismic controlbearing device to make directions of the magnetic fields generated fromthe coil members different from each other.

As can be seen from the foregoing, it is possible for a seismic controlbearing device in accordance with the present invention to activelycontrol various types of dynamic loads generated from the structure byvarying properties of a magneto-sensitive material depending on avariation of a magnetic field. In addition, the seismic control bearingdevice in accordance with the present invention does not need to use alarge amount of power, unlike the conventional active controller, and itis possible to perform the same semi-active control and base isolationperformance as the conventional art through a single seismic controlbearing device, without installing a semi-active controller and a baseisolation device of the conventional art.

Exemplary embodiments of the present invention have been disclosedherein and, although specific terms are employed, they are used and areto be interpreted in a generic and descriptive sense only and not forpurpose of limitation. Accordingly, it will be understood by those ofordinary skill in the art that various changes in form and details maybe made without departing from the spirit and scope of the presentinvention as set forth in the following claims.

1. A seismic control bearing device installed between a ground base anda structure constructed on the ground base to reduce vibration energyapplied to the structure, comprising: a plurality of deposition membersspaced apart from each other; and a plurality of magneto-sensitivemembers disposed between the deposition members and formed of amagneto-sensitive material, wherein properties of including a stiffnesscoefficient and an damping coefficient of the magneto-sensitive materialare varied depending on a variation of a magnetic field formed aroundthe magneto-sensitive member.
 2. The seismic control bearing deviceaccording to claim 1, wherein the magneto-sensitive material comprises arubber matrix formed of rubber, and metal particles dispersed in therubber matrix.
 3. The seismic control bearing device according to claim2, wherein the metal particles are iron particles.
 4. The seismiccontrol bearing device according to claim 3, wherein the depositionmember is formed of a plate-shaped metal material, and themagneto-sensitive member has a plate shape.
 5. The seismic controlbearing device according to any one of claims 1 to 4, further comprisinga core member passing through the deposition members and themagneto-sensitive members and formed of a metal material.
 6. A seismiccontrol system comprising: a sensing unit for sensing dynamic behaviorof a structure and outputting a sensing signal corresponding to dynamicvibration of the structure; a seismic control bearing device installedbetween the structure and a ground base, on which the structure isconstructed, to reduce vibration energy applied to the structure,wherein the seismic control bearing device comprises a plurality ofdeposition members spaced apart from each other, and a plurality ofmagneto-sensitive members disposed between the deposition members andformed of a magneto-sensitive material; a magnetic field forming unitfor generating a variation of a magnetic field in the seismic controlbearing device such that properties including a stiffness coefficientand an damping coefficient of the magneto-sensitive material are varieddepending on the variation of the magnetic field; and a control unit forreceiving a sensing signal from the sensing unit to control the magneticfield forming unit such that the seismic control bearing devicegenerates a seismic control force for reducing vibration energy of thestructure on the basis of the sensing signal.
 7. The seismic controlsystem according to claim 6, wherein the magneto-sensitive materialcomprises a rubber matrix formed of rubber, and metal particlesdispersed in the rubber matrix.
 8. The seismic control system accordingto claim 7, wherein the bearing device further comprises a core memberpassing through the deposition members and the magneto-sensitive membersand formed of a metal material.
 9. The seismic control system accordingto any one of claims 6 to 8, wherein the sensing signal comprisesdisplacement, acceleration, and a vibration cycle of the structure. 10.The seismic control system according to any one of claims 6 to 8,wherein the magnetic field forming unit comprises an annular coil memberdisposed to surround the seismic control bearing device, and a currentsupply part for supplying current to the coil member to form a magneticfield around the coil member.
 11. The seismic control system accordingto claim 10, wherein the control unit controls strength of the magneticfield formed by the magnetic field forming unit by controlling an amountof current supplied from the current supply part.